A. Field of the Invention
The present invention relates to the formulation of mathematical annual accidental and severity prediction models for a variety of applications where conflicts are generated as with human conflict, environmental (possibly weather) conflicts and more specifically in this application with vehicle conflicts for highway intersections and roadway segments, and to the statistical format for each of the submodels which estimate annual angle probable conflict opportunities, annual rear-end probable conflict opportunities, annual side-swipe probable conflict opportunities, and annual fixed object (single vehicle) probable conflict opportunities, and their formulation into a further statistical format which summarizes all of the conflict opportunities into an annual quantity of total probable conflict opportunities which are speed weighted, and using a stable mathematical relationship between speed weighted annual total conflict opportunities and annual accidents, both accurately and with relative precision estimates future annual accidents at any typical highway intersection under any typical traffic volumes, any typical combination of horizontal geometry and lane or bay traffic assignments, and any typical traffic control device including xe2x80x9cNoxe2x80x9d control (driveway), xe2x80x9cYieldxe2x80x9d control, two-way xe2x80x9cStopxe2x80x9d control, four-way xe2x80x9cStopxe2x80x9d control, or signalized traffic control. Using the annual accident estimate for an individual intersection and prior research of the relationship between speed and annual accidents, and fatality or injury involvement, an estimate of future annual fatality and personal injury involvement is also developed which, along with annual accident quantity, can be compared to prior research of the quantity levels associated with acceptable/unacceptable hazard quantity levels for each type of traffic control, and also compared with a quality level associated with an acceptable/unacceptable hazard level for annual personal injury and fatality severities to determine whether the existing and/or a proposed future intersection is or will become hazardous (or incrementally hazardous) by either an inordinate quantity of annual accident occurrences or an inordinate quality (severity) of annual personal involvements. In addition, by summing the estimated annual personal injury and fatality involvement over multiple intersections comprising a highway route and based on the prior researched relationship of route Safety Levels of Service (hazard levels), an entire existing or proposed future highway route can be assessed as either hazardous or non-hazardous (or incrementally hazardous) thereby permitting an entire highway route (as well as any involved intersections) to be examined and/or redesigned to provide acceptable hazard levels. Together with proper engineering judgment, both future highway intersections and routes may be designed interactively by balancing traffic volumes, geometries, and traffic control types against hazard levels to maximize future intersection and highway route safety performance.
Application of the concepts and statistical formulations of this invention are not intended to be restricted to only highway or transportation purposes but may be applicable to other fields of probable event and conflict relationships.
B. Description of the Prior Art
Historically in the transportation field, the only mathematical tools to predict annual accidents have been exposure (rate) based models such as accidents per million entering vehicles for intersections and annual accidents per million vehicle miles of travel for open roadway routes. One attempt to quantify the safety relationship of highway routes using the latter model was published by Jason Yu in October 1972 entitled Establishing Relationship of Level of Service and Highway Safety. 
But neither of these methods are sensitive to the myriad of complexities which affect accident occurrence including the quantity of traffic volumes and their peaking characteristics throughout the day, week and year; the character of the horizontal geometry including the presence of left and/or right turn bays, turning radii, acceleration/deceleration lanes, and median separation from opposing traffic; or the type of traffic controls including no control, yield, two-way stop, all-way stop, or signalized control including the intricate nuances of traffic signal phasing and timings, or the combined effects of roadway and intersection capacity which promote or reduce accidents. In Access Management (designing the spacing of access openings as affected by the character of each access), the problem of reasonably predicting accident expectancies becomes even more complex than the open roadway because of the differences from one access opening to the next given their relative proximity, where the resultant accident expectancies varies depending on the traffic volumes at each independently operating access opening.
Relative precision in the modeling of transportation events has been used many times as an alternative prediction methodology. Probably one of the best known such models is the relative precision model developed by Webster to predict delay at signalized intersections. In Webster""s original model, two distinct types of delay were mathematically hypothesized including 1) Uniform delay and 2) Incremental or random delay. Today, delay models very similar to Webster""s are regarded as the backbone of the Signalized Intersection Chapter of the Highway Capacity Manual (HCM) of the Transportation Research Board. And from these mathematical delay models, Delay-based Levels of Service (LOS) for intersection design and control are used as standard features of both transportation planning and design professions, and for the development of Growth Management in urban areas such as with Florida""s Growth Management Laws. Yet the basic premise for the management of growth and for the design and planning of signalized intersections still rests upon mathematical models which are only relative, and not exact. After all, it is highly unlikely that any one intersection would produce delay results which replicate exactly the delay which the Highway Capacity Manual or Webster""s models predict. From this, it may be seen that the prediction of many values in transportation, whether delay, volumes, or accidents does not rest upon the need for absolute accuracy (because absolute values will always be masked by human, vehicle or environmental factors), but upon the need for realistic accuracy with relative and stable precision.
Several other automobile accident prediction models have been developed in the past, but each of these have focused on the prediction of damage from an accident or with warning a driver of an impending accident location ahead based upon existing accident history with no prediction of future accident history.
U.S. Pat. No. 5,270,708 issued to Kamishima on Dec. 14, 1993, discloses one such model including a position and orientation sensor which forecasts the possibility of occurrence of an accident based on pre-existing accident histories and reiterates throughout that xe2x80x9cpast traffic accident dataxe2x80x9d is stored, extracted and used to discriminate the potential for accidents ahead based on vehicle proximity to an individual accident location, but this model has no capability for forecasting future accidents based on volume, geometric or traffic control changes to the road ahead. U.S. Pat. No. 5,251,161 issued to Gioutsos et al. on Oct. 5, 1993 discloses a method of modeling a vehicle crash wave form to test a crash detection system. U.S.S.R. Patent Document No. 658,575, published on Apr. 30, 1979 to Spichek et al., shows a transport vehicle electronic impact modeling unit for modeling unsurmountable and surmountable obstacles.
U.S. Pat. No. 4,179,739, issued Dec. 18, 1979 to Virnot, discloses a system providing a memory controlled railroad traffic management process. This method regulates the traffic over a network of itineraries travelled by various vehicles such as railroad trains. In addition, several articles have been published drawn to systems and concepts for controlling the flow of traffic, particularly, to reduce the occurrence of traffic jams and/or rear-end collisions. For example, Dickinson et al. published an article in May 1990 entitled An Evaluation of Microwave Vehicle Detection at Traffic Signal Controlled Intersections that discusses monitoring traffic flow however, does not provide any traffic safety models or predictions. Favilla et al. published an article in March 1993 entitled Fuzzy Traffic Control: Adaptive Strategies that discusses the implementation of a logic control system, where the logic is defined by the individual parameters, using the instantaneous traffic flow volumes for generating the traffic light control signals at each intersection in which the system is installed. Harris published an article in August 1994 entitled The Development and Deployment of IVHS in North America, which discusses the historical development of the IVHS in North America, and the prospectus as the turn of the century approaches. Bielefeldt et al. published an article in April 1994 entitled MOTIONxe2x80x94A New On-Line Traffic Signal Network Control System, discussing a specific on-line monitor and traffic flow control system. Hoyer et al. published an article in June 1994 entitled Fuzzy Control of Traffic Lights, that generally describes the implementation of fuzzy logic utilized in a traffic control system. Lee et al. published an article in August 1994 entitled Development and Assessment of a Traffic Adaptive Control System in Korea, describeing the utilization of a coordinated traffic control system over a large spatial area versus individual uncoordinated intersections. Petzold et al. published an article in 1990 entitled Potential for Geographic Information Systems in Transportation Planning and Highway Infrastructure Management, discussing a specific apparatus using spatial analysis for traffic flow control at intersections. Saito et al. published an article in May 1990 entitled Dilemma and Option Zones, the Problem of Countermeasures, describing implementation of a traffic control system utilizing the timing interval of the red/yellow/green lights for reducing rear-end collisions. Kotz et al. published in a textbook in 1983 entitled Educated Guessing, a mathematical algorithm for predicting the probability of a specific group of variables.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed. Thus there exists no Prior Art with respect to the formulation of mathematical models which interactively predict annual accidents, severities and hazard levels at a highway intersection simultaneously for present or estimated future traffic volume levels, for present or estimated future horizontal geometric conditions, and for present and estimated future traffic control types, nor is there any Prior Art with respect to the application of the annual future severity estimates to examine the existing or estimated future hazard levels associated with either an individual intersection or a highway route composed of a number and variety of alternate intersection types.
Numerous studies have reported on the impacts, effects, and correlation of conflicts to accidents at specific intersections and roadways, with most finding weak correlation to accident occurrence. This is not unexpected in the modeling of conflicts because the recordation of a conflict occurrence is generally developed from the observation of an on-road brake light application where the driver""s brake light pedal pressure is unique among drivers and influenced and confounded by human, vehicle and environmental factors and effects. Because of this, actual on-road conflicts are often inconclusive as accident surrogates, and it becomes necessary to develop a more precise and stable formulation of conflict occurrence.
Statistical formulations of events in highway engineering over the last several decades has become an area of significant involvement because of the size of databases available and the ability of statistics to be placed in microcomputer formats for use by planning and design personnel. In mathematical accident modeling using xe2x80x9cper million entering vehiclesxe2x80x9d or xe2x80x9cper million vehicle miles of travelxe2x80x9d, statistics have become an essential part of the process in determining whether improvements have had a significant effect on prior accident occurrence. This acceptance of statistical concepts can also permit planning and design personnel to understand that actual (on-road) conflicts can be replaced by statistical (off-road) conflicts. For purposes of this modeling, the formulation of statistical (off-road) conflicts are referred to as Statistically Probable Conflict Opportunities (SPCO""s) or more simply Probable Conflict Opportunities (PCO""s).
The object of the present invention is to provide for traffic engineering and transportation planning professionals a mathematical model to examine the existing hazard levels of highway intersections and routes, and for designing safety into intersection and highway route project design before construction by accurately estimating the annual accident and severity effects of alternative intersection designs and highway route intersection spacing strategies to provide for optimal safety and minimize the development of hazardous safety levels within the design life of the highway intersection or route project.
To achieve the above-mentioned object, the mathematical models and their formulations use a finite element analysis approach and break the accident models, each intersection, and each highway route into discrete elements comprised of: (a) four similarly formatted accident models (angle, rear-end, side-swipe, and fixed object) each of which use discrete elements such as lanes, turnbays, traffic control type, and traffic flow rates (based on normalizing assumptions regarding drivers, vehicles and environments) to create a new and unique statistical likelihood that two separate vehicles will be on intersecting and conflicting paths of advancing and opposing vehicles but only for a finite and discrete period of time (using prior research of the conflict exposure relationship as a function of specific intersection and other characteristics) which thereby creates the opportunity for conflict and defines a Statistically Probable Conflict Opportunity, (b) where for each of the above Statistically Probable Conflict Opportunity models, the conflict is defined as the statistical union of the probability of two assumed mutually exclusive events including 1) the probability of vehicle arrival for a particular movement, and 2) the probability of vehicle opposition to the arrival with both probabilities using the Poisson Distribution or similar statistical distribution but only during the period of time the arriving vehicle is exposed to conflict, which is a significant difference of the SPCO mathematical formulations from any prior accident and conflict modeling relationship, (c) a mathematical format which uses speed-based weightings calibrated to actual accidents to sum each of the above four probable conflict opportunity mathematical model estimates into a total summed annual conflict opportunity estimate, and from this summation to determine annual accidents using a stable linear mathematical relationship between total summed annual probable conflict opportunities (regardless of type) and total annual accidents at an intersection as a function of traffic control type {which is referred to as the Access Management Accident (AMA) Model}, (d) a surrogate exposure-based accident mathematical model for use with Fixed Object (single vehicle) annual accidents to simplify Fixed Object annual accident estimation in lieu of measuring the location and type of each physical feature adjacent to each intersection approach or roadway, (e) mathematical models created from prior research to estimate annual fatality and personal injury involvement given the speed of operation and annual accident involvements at an intersection, (f) mathematical comparisons of annual accident quantity with prior research of quantity-based hazard definitions, (g) mathematical comparisons of annual personal injury and fatality (quality/severity) involvement with a user defined severity-based hazard definition which, with the above hazard quantity indicator, can be used to examine and/or design hazard levels at individual intersections, and (h) summing estimated future fatality and injury involvement from multiple intersections to form a composite severity measure for a highway route, which, with normalizing national accident statistics for each state, can be used with prior research to provide nationally comparable mathematical comparisons of highway route, and even Statewide hazard levels, for existing and/or projected future conditions as affected by changes in traffic volumes, geometries and/or traffic control devices.
xe2x80x9cSafe or Unsafexe2x80x9d, and hazard levels associated with these, are perceptions viewed differently by each highway driver based on psychological and physiological conditioning at a particular point in time and under conditions which are constantly changing. Given that this perception is variable to the driver and influenced by the vehicle and the environment, the absolute threshold of safe/unsafe or hazardous/not-hazardous can never be set with precision for an individual driver. However, xe2x80x9cApparent Thresholds of Safety or Hazardxe2x80x9d may be used as indicators of actual levels where the apparent threshold appears as either a widely accepted standard or where logic suggests a reasonable threshold. In a traditional definition, xe2x80x9cHazardxe2x80x9d is composed of two mutually exclusive elements either of which may independently cross the threshold from xe2x80x9csafe to unsafexe2x80x9d. The first of these elements is xe2x80x9cdangerxe2x80x9d or the exposure to risk which is a quantity-based element, and the second is xe2x80x9charmxe2x80x9d which is a quality-based physical or psychological injury or a severity characterization of danger without respect to quantity. Thus a xe2x80x9cGenerally Hazardous or Unsafexe2x80x9d condition may be defined by either:
1. An overt number of unacceptable events (accidents) per unit timexe2x80x94One of the most long-standing and accepted apparent hazard thresholds is that provided by the xe2x80x9cAccident Experience Warrantxe2x80x9d (#6) of the Manual of Uniform Traffic Control Devices (MUTCD-USDOT) which provides that where annual accidents correctable by the presence of a traffic signal exceed 5 per year, a xe2x80x9cStopxe2x80x9d controlled intersection may be converted to signalized control. In a similar manner, prior research of traffic control types has indicated that where xe2x80x9cYieldxe2x80x9d traffic control exists annual accidents should not exceed 0.66 accidents per year, and where xe2x80x9cNoxe2x80x9d traffic control (driveway) exists annual accidents should not exceed 0.33 accidents per year. Threshold hazard quantity indicators do not exist for xe2x80x9cAll-Way Stopxe2x80x9d control or for signalized intersection control where the quality or severity of hazard generally define acceptable or hazardous operating conditions, or
2. One event where the quality of the event (accident) is so severe as to be unacceptablexe2x80x94The outcome of any one accident may result in a combination of property damage, personal injury and/or fatality to one or more occupants where neither property damage nor personal injury may provide an adequate characterization of accident quality. However, where an individual fatality occurs, it may be said with certainty that had the person known the trip would result in death, there is little doubt the trip would not have occurred, unless the intent was fatal, which cannot by definition conform to the assumption of a normal driver. Barring intentional death, a fatality is one outcome of an accident which is unacceptable under all circumstances, and from this a severity threshold criterion can be established which provides that xe2x80x9cNo driver or passenger should die as a result of an auto accident in their lifetimexe2x80x9d. Assuming a conservative lifetime of 100 driving years (approximately 115 years of age) and only one occupant per vehicle (a conservative approach to safety threshold definition), using this definition no intersection should produce an annual fatality estimate which exceeds 0.01 per year, or 1 fatality in 100 years of intersection operation. Since from national accident statistics, the average auto occupancy in injury accidents is approximately 2.0 and given the fatality:injury ratio in an injury accident is approximately 1:37, and that the difference between a personal injury and a fatality may be age, health or more simply xe2x80x9cbad luckxe2x80x9d dependent phenomena, a more conservative approach to the definition of a safe/unsafe severity threshold is to include not only estimated fatalities, but also personal injuries in the threshold definition, such that a reasonable threshold for accident Severity may be where estimated annual personal injuries and fatalities exceed 0.75 per year (0.01*2*(37+1)) However, the selection of life duration, auto occupants and fatality:injury ratio are user defined phenomena which will affect the severity threshold definition and subsequent incremental hazard Levels of Service.
Having defined an adequate xe2x80x9cSafe/Unsafexe2x80x9d threshold for an individual intersection above (composed of both quantity and quality-based phenomena) and assuming adequate model validation to local environmental areas, driving populations, and vehicle types, the severity estimate of individual intersections may be summed over a pre-defined (existing or proposed) distance which contains all of the intersections and compared to prior research of Route Safety Hazard Levels (Jason Yu, October, 1972) to determine whether a particular route over a specified distance contains an inordinate quantity of severities as adjusted by reference to national accident and other statistics to account for urban/rural, interstate, and environmental factors which permit normalization of the variety of factors affecting hazard level thresholds.
Using the above thresholds for safe/unsafe, hazardous/non-hazardous intersection and highway route safety performance, both Intersection Safety Levels of Service (ISLOS) and Route Safety Levels of Service (RSLOS) may be defined with both numerical and/or alphabetic assignments from A-F representing each of the various safety/hazard levels from excellent and safe (A) to unacceptable and unsafe (F) in a manner similar to the Levels of Service identified by the Highway Capacity Manual of the Transportation Research Board.
Accordingly, it is a principal objective of the invention to provide a prediction model for forecasting the expected number of accidents at an existing or proposed intersection or series of intersections.
It is another objective of the invention to provide a prediction model for forecasting the relative impact of a proposed change to an intersection on the number of accidents or severities at an existing or proposed intersection or series of intersections.
It is a further objective of the invention to provide a prediction model for forecasting the effects on traffic and accident/severity levels in an area by adding, replacing, or removing intersections or intersection features to a roadway.
Still another objective of the invention is to provide a prediction model which rates intersections and highway routes in terms of accidents, severities and hazard levels which can be used to compare safety levels between disparate geographic areas.
And it is an objective of the invention to provide improved elements and arrangements thereof in an apparatus for the purposes described which is inexpensive, dependable, stable and fully effective in accomplishing its intended purposes.
These and other objects of the present invention will become readily apparent upon further review of the following specifications and drawings.